Electron guns



March 27, 1962 R. E. BENWAY ELECTRON GUNS Filed June 27, 1958 IINVENTOR Ruszm" E. BENYIAY United States Fatent @fine 3,027,479 Patented Mar. 27, 1962 3,027,479 *LECTRON GUNS Robert E. Benway, Marion, Ind, assignor to Radio Corporation of America, a corporation of Delaware Filed June 27, 1953, Ser. No. 745,066 Claims. (Cl. 313-82) This invention relates to electron discharge devices and particularly to the mounting of the electrodes in elec tron guns of the type employed in television picture tubes and other cathode ray tubes.

An electron gun of the type conventionally employed in cathode ray tubes consists of a plurality of axially spaced electrodes to which are applied various operating potentials to form electron lenses. Electron emission from a cathode electrode of the gun is formed into an electron beam and focussed on a phosphor viewing screen by the lenses.

The trend to larger television viewing screens has made it necessary to increase the front-to-back dimension or length of the picture tube. Since longer tubes necessitate deeper cabinets an effort has been made to reduce tube length in order to provide a television cabinet having better appearance.

The length of the tube may be reduced by using wider angle deflection of the electron beam so that the electron gun can be positioned closer to the face plate of the tube. There are, however, practical limits to which the angle of deflection may be increased by reason of deflection power requirements, minimum spot distortion and size and scanning raster shape.

The length of the picture tube may also be reduced by shortening the electron gun. When the electron gun is shortened, more accurate alignment of the various elec trodes of the electron gun is essential in order to minimize beam distortion in the principal focusing field and in the deflection field. Both the axial dimensions of the gun electrodes and their axial spacings may be made smaller. This necessitates the provision of better insulation between the electrodes.

It is an object of this invention to provide an improved electron gun.

Another object of this invention is to provide an electron gun having a minimum overall length.

Still another object of the invention is to provide an electron gun having minimum leakage paths for high potentials and yet whose structure is sufliciently stable to permit the use of electrodes having small dimensions and minimum spacing.

According to the present invention an electron gun includes a pair of electrode sub-assemblies, one of the sub-assemblies being supported by insulating rods and another of the sub-assemblies being supported by metal straps. The sub-assemblies are fastened together by having one electrode common to both the insulating rods and the metal straps. In certain forms of the invention the metal straps are C-shaped and permanently distortable which enables an accurate spacing adjustment of the electrodes before final assembly.

The invention is illustrated in the accompanying drawing of which:

FIGURE 1 is a side view, partially in section, of a television picture tube;

FIGURE 2 is a sectional view of the tube neck showing the location and structure of an electron gun;

FIGURE 3 is a view taken on sectional line 3-3 of FIGURE 2 and shows the displacement angles of the electrode support elements;

FIGURE 4 is an enlarged sectional view of an electron gun taken along line 4-4 of FIGURE 2; and

FIGURE 5 shows a modified form of an accelerating electrode.

In the various figures of the drawing the same numeral is used to designate the same element.

FIGURE 1 shows a complete cathode ray tube particularly adapted for the reproduction of television images. The tube envelope consists of a neck portion 11 joined to a bulb portion 13 and a glass face plate 15. An electron gun 17 is contained within the tube neck portion 11 to provide an electron beam which is directed and focussed onto the phosphor screen B on the interior of the face plate 15. The phosphor screen 19 consists of a thin film of phosphor material which will luminesce to provide visible light when bombarded by an electron beam. The electron beam is scanned over the phosphor screen 19 in a rectangular raster by a deflection yoke 21. A tube base 23 has metal prongs 25 which are adapted to engage an appropriate tube socket of the television receiver. The metal prongs 25 are connected to the electrodes of the electron gun 17.

A conductive wall coating 27 is formed on the inner surface of the tube bulb portion 13 and extends from the tube neck portion 11 to a point adjacent the phosphor screen 19.

FIGURE 2 shows an enlarged view of the configuration of the electron gun 17 and its placement in the tube neck portion 11. The electron gun 17 consists of the following electrodes reading from left to right in FIGURE 2 of the drawing: cathode electrode 29, control electrode 31, first accelerating electrode 33, second accelerating electrode '35, focusing electrode 37 and third accelerating electrode 39.

The various electrodes of the electron gun 17 are supported and properly spaced from each other in the tube neck portion 11 by the tube lead-ins 4 1, a pair of glass rods 43 and a pair of metal straps 45. The electron gun 17 is held on the axis of the tube neck portion 11 by spring spacers 47. The spring spacers 47 also make electrical contact with the conductive wall coating 27. A getter 49 is supported by the third accelerating electrode 39.

FIGURE 3 is a sectional view of FIGURE 2 along the lines 33. The angular placement of the glass rods 43 and the metal straps 45 is clearly shown in FIGURE 3.

FIGURE 4 shows, in detail, the construction of the various electrodes of the electron gun 1'7 and the manner in which the electrodes are attached to the glass rods 43 and the metal straps 45.

The cathode electrode 29 consists of a small metal tube 51 closed at its right end by a wall portion 53. The outer surface of the cathode wall portion 53 is coated with a thermionic emitting material consisting, for example, of a mixture of barium and strontium oxides. A cathode heater filament 55 is mounted within the metal tube 51 for maintaining the thermionic emitting material on the cathode wall portion 53 at an elevated temperature. At elevated temperatures the thermionic emitting material provides a source of electrons.

The cathode electrode 29 is mounted in a ceramic disk 57 which is rigidly supported within the control electrode 31. The control electrode 31 consists of a cylinder portrode 31.

The second accelerating electrode 35 consists of a funnel shaped member 69 and a. tubular member 71. The funnel shaped member 69 of the second accelerating electrode -35 extends into the first accelerating electrode 33. The tubular member 71 of the second accelerating electrode {35 includes an apertured reentrant portion 73 on its righthaiid end. The funnel shaped member 69 and the tubular inernber 71 of the second accelerating electrode 35 are -telescoped with each other and welded together after careful spacing adjustment.

The third accelerating electrode 3'9 is closed at its left end by an apertured reentrant portion 75. The apertured reentrant vportion 73 of the second accelerating electrode 35 and the apertured reentrant portion 75 of the third accelerating electrode 39 are enclosed by focusing electrode 37 to form an electron lens. The focal length of the lens is dependent on the spacing between accelerating electrodes 35 and 39 and the potential applied between the focusing electrode 37 and the accelerating electrodes 35 and 3.9.

A disk shaped element 77 forms a part of the third accelerating electrode 39.

The control electrode 31, first accelerating electrode 33, second accelerating electrode 35 and the focusing electrode 37 are each attached to the glass rods 43 by supporting studs 79 which are embedded in the glass rods 43 and welded to the various electrodes.

The second accelerating electrode 35 and the third ac= 'celerating electrode 39 are supported by metal straps 45-. The metal straps 45 are welded to the outside of the second accelerating electrode 35, the inside of the third accelerating electrode 39 and the left side of the disk shaped element 77-. The C shape of the metal straps 4-5 permits the straps 45 to encompass the right end of the third accelerating electrode 39 and at that point be welded to the disk shaped element 77. Particular attention is invited to the fact that the second accelerating elecrode 35 is fastened to the glass rods 43 and the metal straps 45. Since the second accelerating electrode 35 is common to both the first assembly of electrodes supported by the glass rods 43 and the second assembly consisting of the electrodes supported by the metal straps 45, all of the electrodes of the electron gun 17 are maintained in a predetermined position with respect to each other.

Since the metal straps 45 are permanently distortable, the separation between the second accelerating electrode 35 and the third accelerating electrode 39 may be preadjusted before a final assembly of the electrodes of the electron gun 17.

In the manufacture of the electron gun 17 supporting studs 79 are welded to the outsides of electrodes 31, 33, 35 and 37.

A subassembly of second accelerating electrode 35 and third accelerating electrode 39 is constructed by placing the electrodes 35 and 39 in a jig and welding metal straps 45 to the outside of second accelerating electrode 35 and the inside of the third accelerating electrode 33. The jig provides accurate alignment and spacing of the second accelerating electrode apertured reentrant portion 73 with respect to the third accelerating electrode apertured reentrant portion 75.

The second accelerating electrode funnel shaped member 69 is then inserted in the second accelerating electrode tubular member 71 and welded at its proper position with respect to the second accelerating electrode apertured reentrant portion 73.

The subassembly consisting of the cathode electrode 29, control electrode 31, first accelerating electrode 33, second accelerating electrode 35 and focusing electrode 37 is then assembled by first threading the focusing electrode 37 into the previously fabricated subassembly consisting of the second accelerating electrode 35 and the third accelerating electrode 39. The hook on the right hand side of the C-shaped metal straps 45 permit the threading of focusing electrode 37 into the subassembly consisting of the second accelerating electrode 35 and the third accelerating electrode 39. Electrodes 31, 33, 35 and 37 are then placed in a jig and the supporting studs 7% are embedded into the glass rods 43 after the glass rods have been heated.

Tube lead-ins 4d are Welded to the supporting studs 79 attached to the control electrode 31. Tube lead-ins 41 support the left end of the electron gun 17. When the electron gun is inserted in the tube neck is rtion ll of the cathode ray tube the spring spacers 47 support the electron gun l7 and provide an electrical connection between conductive wall coating 27 and the third acce1erating electrode 39.

The subassemblies supported by glass rods 43 and metal straps 45 provide for efficient manufacture of the electron gun 17. By having at least one electrode, such as the second accelerating electrode 35, common to both subassemblies the two subassembiies may be conveniently assembled together.

By employing metal straps 45, an electrical connection is provided between the second accelerating electrode 35 and the third accelerating electrode 39. The disk shaped element 77 is electrically connected and mechanically fastened to the cylindrical portion of the third accelerating electrode 39. The G shape of the metal straps 45 permits threading of the focusing electrode 37 into the subassembly consisting of second accelerating electrode 35 and third accelerating electrode 39.

A minimum number of leakage paths between electrodes are provided.

In FIGURE 5 there is shown another form of accelerating electrode which is adapted to replace the third ac celerating electrode 39 and the disk shaped element 77 of the form of the invention shown in FIGURE 2 and 4. The third accelerating electrode 39 and the disk shaped element 77 are combined into a single element with a cylindrical portion 81 and a flanged portion 83. The C- shaped metal straps 35 are Welded to the rear of the flanged portion 83.

Having thus described the invention, what is claimed is:

1. An electron gun assembly for a cathode ray tube including in the order named and in alignment a cathode electrode, control grid electrode, first and second accelerating electrodes, a focusing electrode, and a third accelerating electrode, said second accelerating, focusing and third accelerating electrodes forming an electrostatic lens, all of said electrodes except said third accelerating electrode being insulatingly supported in spaced relationship by a plurality of insulating rods extending parallel to the axis of said assembly, and a plurality of electrically conducting elongated elements connected to said second and third accelerating electrodes to support said third accelerating electrode from said second accelerating electrode, said elongated elements being displaced circumferentially with respect to said insulating rods.

2. An electron gun assembly for a cathode ray tube including in the order named and in alignment a cathode electrode, control grid electrode, first and second accelerating electrodes, a focusing electrode, and a third accelerating electrode, said second accelerating, focusing and third accelerating electrodes forming an electrostatic lens, all of said electrodes except said third accelerating electrode being insulatingly supported in spaced relationship by a plurality of insulating rods extending parallel to the axis of said assembly, a plurality of electrically conducting 'C-shaped metal straps connected to said second and third accelerating electrodes to support said third accelerating electrode from said second accelerating electrode, said metal straps being displaced circumferentially with respect to said insulating rods, said third accelerating electrode consisting of a cylindrical portion and a flanged portion at right angles to the axis of said cylindrical portion, and wherein said electrically conducting -Cshaped metal straps are fastened to the flange portion of said third accelerating electrode.

3. An electron gun for a cathode ray tube, said electron gun comprising a plurality of electrode assemblies, one of said assemblies including a plurality of axially spaced electrodes fastened to and mutually supported by a plurality of insulating rods, another of said assemblies including a plurality of axially spaced electrodes fastened to and mutually supported at least in part by a plurality of metal straps, and wherein one of said electrodes is fastened to and supported by both insulating rods and metal straps.

4. An electron gun for a cathode ray tube, said electron gun comprising a pair of electrode assemblies, one of said assemblies including a plurality of axially spaced electrodes fastened to and mutually supported by a plurality of insulating rods, another of said assemblies including a plurality of axially spaced electrodes fastened to and mutually supported by a plurality of metal straps, said metal straps being permanently distortable, (Z-shaped and having their free ends fastened to each of two electrodes, and one of said electrodes being fastened to and supported by both insulating rods and metal straps.

5. An electron gun for a cathode ray tube, said electron gun comprising a pair of electrode assemblies, one of said assemblies including a plurality of axially spaced cylindrical electrodes fastened to and supported by a plurality of insulating rods, another of said assemblies including a plurality of axially spaced cylindrical electrodes fastened to and supported by a plurality of metal straps, one of said electrodes being fastened to and supported by both said insulating rods and said metal straps, each of said metal straps having one end fastened to the outside of a first cylindrical electrode and the other end of each metal strap fastened to the inside of a second cylindrical electrode, said metal straps extending around the edge of said second cylindrical electrode remote from said first cylindrical electrode, and a disk shaped electrode axially spaced from said cylindrical electrodes and also fastened at one of its sides to said metal straps at a point where said metal straps extend around the edge of the cylindrical electrode.

6. An electron gun for a cathode ray tube, said electron gun comprising a plurality of electrodes, a pair of glass rods supporting some of said electrodes in axially positioned relationship, a pair of metal straps supporting some of said electrodes in axially positioned relationship, and wherein one of said electrodes intermediate the end electrodes is fixed to both of said glass rods and to both of said metal straps.

7. An electron gun for a cathode ray tube, said electron gun comprising a plurality of spaced electrodes including two accelerating electrodes adapted to be operated at a relatively high potential and an intermediate focusing electrode adapted to be operated at a relatively low potential, metal support strap means connected only to and mutually supporting said two accelerating electrodes and insulating support rod means connected to and mutually supporting all electrodes except one of said accelerating electrodes.

8. An electron gun for a cathode ray tube, said electron gun comprising a plurality of spaced electrodes including first, second and third electrodes, said first and third electrodes adapted to be operated at a relatively high potential, said second electrode adapted to be operated at a relatively low potential, metal support strap means connected only to and mutually supporting said first and third electrodes, and a pair of insulating support rods both of which are connected to and mutually support all electrodes except said third electrode.

9. An electron gun comprising at least one elongated insulating support member, a first plurality of electrodes mutually supportingly mounted on said at least one elongated insulating support member, at least one elongated conductive support member, and a second plurality of electrodes mutually supportingly mounted on said at least one elongated conductive support member, and wherein at least one electrode of said first plurality of electrodes constitutes one of the electrodes of said second plurality of electrodes.

10. An electron gun comprising a plurality of electrode assemblies, one of said assemblies including at least one elongated insulating support member and a first plurality of axially aligned electrodes mounted in mutually sup= ported spaced relation on and along said at least one elongated insulating support member, another of said assemblies including at least one elongated conductive sup port member and a second plurality of axially aligned electrodes mounted in mutually supported spaced relation on and along said at least one elongated conductive support member, and wherein at least one electrode is common to both said electrode assemblies.

References Cited in the file of this patent UNITED STATES PATENTS 2,723,362 Gethmann Nov. 8, 1955 2,732,511 Dichter Jan. 24, 1956 2,792,515 Broderick et al. May 14, 1957 2,840,739 Lesoviez June 24, 1958 2,853,639 Knochel et a1 Sept. 23, 1958 2,911,563 Atti et a1. Nov. 3, 1959 

